1. Field of the Invention
The invention relates to a spirally wrapped elongated structure, a method of manufacturing the wrapped elongated structure and an apparatus for manufacturing the wrapped elongated structure. More particularly, the invention relates to an electrical conductor core spirally wrapped with insulating tape which is in contact with an adhesive tape extending along the core, a method of wrapping an electrical conductor core with insulating tape in contact with adhesive tape and an apparatus for wrapping an electrical conductor core with insulating tape in contact with adhesive tape. The adhesive tape adheres to the spirally wrapped insulating tape and thereby maintains the spiral formation of the insulating tape during forming or cutting of the conductor.
2. Descriptions of the Prior Art
Conductors spirally wrapped with tape material are commonly usd in electrical equipment. More in particular windings of power transforms can comprise conductors which are spirally wrapped with layers of insulating tape. Thus, in a typical application the wrapped conductors are separated by the wrapping and are electrically insulated from one another by the tape wrapping and by transformer oil surrounding the conductors. In such an application the tape material can be rope fiber which comprises approximately 90% hemp material and 10% pulp material, draft paper, or other suitable insulating materials. Thermally upgraded rope fiber material and various other papers which can withstand a moderately high temperature rise can also be used. In addition, where higher temperatures are encountered, the conductors can be wrapped with tape insulating material, which consists of nylon fibers, a type of which is marketed by E.I. DuPont DeNemours of Wilm., Del., under the trademark NOMEX.
The prior art commonly discloses conductors wrapped in insulating tape. In U.S. Pat. No. 3,886,316 which issued on Feb. 18, 1975 to Takechi et al, a conductor is insulated by placing a string of resin material extending along the length of the conductor, spirally wrapping the conductor and string with insulating tape, impregnating the wrapped conductor with resin material and heating the conductor to fuse the string with the impregnating resin. The resin string served to create interstices in the wrapping to collect resin. After heat treatment, the impregnated resin, the resin string and the wrapping become a solid insulating layer. U.S. Pat. No. 3,575,748 issued to Polizzano teaches a method for insulating conductors wherein a narrow tape placed along the length of a conductor and the conductor is enveloped in an insulating sleeve with the longitudinal edges overlapping on the narrow tape. The overlapping edges and the narrow tape are then heat sealed to form a solid insulating layer.
The prior art also includes U.S. Pat. No. 3,873,396 which issued on Mar. 25, 1975 to Rice. This patent shows a method for coating a pipe by spirally wrapping a web around the outside of the pipe. As the web is wrapped, an adhesive is applied to one edge of the top surface of the web in order that the layer of adhesive is interposed between the top side of one wrap of tape and the bottom side of the next overlapping wrap of tape. This construction holds the tape in its spiral orientation around the pipe and prevents separation of adjacent wraps of tape. Thus, a solid layer is formed around the pipe.
U.S. Pat. No. 3,687,778 issued on Aug. 29, 1972 and U.S. Pat. No. 3,761,335 issued on Sept. 25, 1973, each to Chichoski et al, teach the applying of an adhesive to the outside surface of a tubular member and then spirally wrapping the member with a webbing. The adhesive on the outside surface of the tubular member causes the webbing to adhere directly to the tubular member and form a solid layer of webbing around the tubular member.
The prior art also teaches methods of creating tubular articles from spirally wound webs. U.S. Pat. No. 3,468,733 which issued on Sept. 23, 1969 to Dunlap, Jr. et al discloses a method of making tubular articles by spirally winding a narrow one-sided adhesive strip around a mandrel with the adhesive facing away from the mandrel and spirally winding a paper strip on the same mandrel over the adhesive strip. The adhesive strip underlies the edges of two adjacent wraps of paper webbing and thereby holds the tubular shape of the article.
U.S. Pat. No. 3,457,130 which issued on July 22, 1969 to Morrison discloses a method and apparatus for making tubular articles from spirally wound paper tapes. In Morrison, a narrow strip of thermoplastic material is spirally wound around the mandrel underlying adjacent edges of spirally wound plies of paper thermoplastic laminates. The outside surface of the thermoplastic materials when heated effects a bond between the edges of adjacent strips of material to bind the object in its tubular shape.